Plant Taxonomy

What is a Plant? A Traditional View


  • Plants are characterized by their characters & character states
    • green
    • non-motile
    • eukaryotic & multi-cellular
    • walls of cellulose
    • alternation of generations



  • Diversity: There are many kinds of plants and hundreds of thousands of species
    • But the basic lineages of plants are fairly easy
    • new characters define evolution of lineages

Taxonomy


  • Classification is putting objects into groups
    • requires naming, describing, and identifying species
    • “science of documenting biodiversity” (Keogh, 1995)


  • Linnaeus founded binomial system and classification hierarchy
    • King Phillip Came Over From Germany Stoned
    • each level or unit is called a taxon w/ standardized endings


  • Kingdom is most inclusive group, species is least inclusive
    • in your generation these hierarchies may become obsolete via molecular markers

Taxonomy has predictive value…


  • Question: If two plants are related (i.e., in the same genus) and one of the plants is a source of food or drug, what can we assume about the second plant?


  • Case Study: Pacific yew (Taxus brevifolia)
    • Taxol: alkaloid first isolated from the bark and used to treat breast cancer
    • FDA approval in 1994 but the bark of 3 trees is needed for 1 patient
    • 16,000 pounds of bark is used to produce 2.2 pounds of taxol


  • Search for taxol was successful in other members of the genus
    • has made drug more available

Nomenclature

Common names vs Scientific nomenclature


  • Common names have the following advantages:
    • often descriptive (i.e., describe some important feature)
    • easy to pronounce & remember (more familiar to people)
    • more pleasing to hear & some are fun


  • Common names have some disadvantages:
    • not governed by rules, so little consistency
    • applied indiscriminately to various taxonomic levels (i.e. ‘Oak’)
    • some plants have more than one common name
    • may not exists for rare species
    • may reflect language barriers
    • may be botanically incorrect (e.g. Jerusalem artichoke)

Common names vs Scienitific nomenclature



  • The rule book for botanical nomenclature is the International Code of Botanical Nomenclature (ICBN)
    • every plant gets 1 binomial name
    • Binomials are genus name + specific epithet (e.g. Quercus rubra)


  • Genus names are nouns that may commemorate a place, person, person, habitat, culture
  • Epithets are adjectives that can also be commemorative (except for you!)


  • Taxonomic ranks have standardized endings

Identifying a species usually requires a dichotmous key



  • Keys consists of paired questions (‘couplets’)
    • resembles choose your own adventure books
    • choose the statement that fits your specimen
    • guides you forward through selection steps


  • We will need to bypass this process in this class
    • we will utilize online tools that help
    • phone apps and interactive keys


  • I want you to learn major diagnostic characters

We must learn vegetative terminology!!




  • The amount of terminology used in Plant Taxonomy may, at times, seem overwhelming


  • A feature of a plant is called a character and the specific form of the character is a state.


  • First, we focus on vegetative (non-reproductive) parts
    • includes the 3 primary organs - leaf, root, stem
    • you will need many states to ID a plant!

Life span/Duration:


  • Annual: completes life cycle in a single year
  • Biennial: completes life cycle in two years
  • Perennial: lives more than two seasons


  • Evergreen: keeps its leaves year-round
  • Deciduous: looses its leaves at the end of growing season


  • Hard to determine what a herbaceous plant is…
    • annuals have small slender taproots, while biennials/perennials are larger.
    • biennials & perennials often have storage structures (bulbs)
    • plants with woody stems are perennials

Plant vegetative organs (only 3! plants are easy!)



  • Root: anchor and absorbs, underground, develop from radicle in seed


  • Leaf: photosynthetic organ, attached to stem, has a bud at its base


  • Stem - leaf-bearing organ, with buds


  • Some plants lack one or more of these structures
    • aquatic plants often lack roots and cacti lack leaves.

Leaf parts




  • Blade - main photosynthetic part


  • Petiole - a bontany term for the stalk of the leaf


  • Stipules - appendage at base of petiole in some leaves
    • Stipules can be glandular, leafy, spiny, or scale-like
    • Often, stipules fall off after the leaf expands

Leaf structure


  • simple - leaf blade all one section


  • compound - leaf blade divided into smaller sections
    • leaflet - section of a compound leaf


  • rachis - stalk that supports leaflets in a compound leaf
    • on central axis
    • rachilla - stalk that supports lateral leaflets


  • pinnately compound - like a feather


  • palmately compound - like the fingers on your hand

Leaf Arrangement




  • Leaves may be found at base (e.g. dandelion), along the stem, or both




  • Leaves are attached at nodes:
  1. alternate - one leaf per node
  2. opposite - two leaves per node
  3. whorled - more than two leaves per node; not common in temperate woody plants

Trees with opposite leaves = MADCAP HORSE





  • M=maple; A=ash; D=dogwood


  • CAP=Caprifoliaceae or Honeysuckle family


  • Horse = Horsechestnut and buckeye

Leaf margin





  • entire: margin smooth


  • lobed: margin with indentations


  • serrate: margin toothed
    • Singly or doubly toothed

Leaf shape: There are sooooo many


Leaf Venation




  • pinnate: single main vein with secondary veins branching
    • like a feather


  • palmate: several primary veins arising from a one point


  • parallel: primary & secondary veins parallel

Surface features




  • glabrous - no hairs, smooth surface


  • pubescent - hairy; due to trichomes


  • glaucous - powdery covering


  • scabrous - rough to the touch like sandpaper

Stem features

  • Node: region where leaf is attached
    • internode - region between nodes
    • axil - upper junction of leaf and stem


  • Bud - embryonic shoot and/or flowers
    • found in the leaf axil; at the base of leaf
    • axillary/lateral: buds along stem
    • terminal: buds at the end of the stem
    • scales: protective covering over bud


  • Terminal bud scale scar: left on stem where the terminal bud scales fell off
    • count to determine age of twig


  • Leaf scar: left on stem where leaf detached

Know your bark!


Get collecting!!



  • 40 pressed specimens
    • plant presses must stay in SS 303
    • use ‘Seek’ app or other to ID


  • 40 drawings in your field guide
    • include a table of contents
    • add character guide in your sketchbook
    • sketch each leaf and other characters
    • list the diagnostic characters
    • 2-3 ecological/cultural facts

Web Resources and Plant ID apps